The invention relates to gas-permeable membranes suitable for use in the packaging of respiring biological materials.
Respiring biological materials, e.g. fruits and vegetables, consume oxygen (O2) and produce carbon dioxide (CO2) at rates which depend upon the stage of their development, the atmosphere surrounding them and the temperature. In modified atmosphere packaging (MAP), the objective is to produce a desired atmosphere around respiring materials by placing them in a sealed container whose permeability to O2 and CO2 is correlated with (i) the partial pressures of O2 and CO2 in the air outside the package, and (ii) the temperature, to produce a desired atmosphere within the container. In many cases, the container includes an atmosphere control member (ACM) having a high O2 transmission rate (OTR) and CO2 transmission rate (COTR). In controlled atmosphere packaging (CAP), the objective is to produce a desired atmosphere around respiring materials by displacing some or all of the air within a container by one or more gases, e.g. nitrogen, O2, CO2 and ethylene, in desired proportions. For further details of MAP and CAP, reference may be made, for example, to U.S. Pat. No. 3,360,380 (Bedrosian), U.S. Pat. No. 3,450,542 (Badran), U.S. Pat. No. 3,450,544 (Badran et al.), U.S. Pat. No. 3,798,333 (Cummin et al), U.S. Pat. No. 3,924,010 (Erb), U.S. Pat. No. 4,003,728 (Rath), U.S. Pat. No. 4,734,324 (Hill), U.S. Pat. No. 4,779,524 (Wade), U.S. Pat. No. 4,830,863 (Jones), U.S. Pat. No. 4,842,875 (Anderson), U.S. Pat. No. 4,879,078 (Antoon), U.S. Pat. No. 4,910,032 (Antoon), U.S. Pat. No. 4,923,703 (Antoon), U.S. Pat. No. 4,987,745 (Harris), U.S. Pat. No. 5,041,290 (Wallace et al.) U.S. Pat. No. 5,045,331 (Antoon), U.S. Pat. No. 5,063,753 (Woodruff), U.S. Pat. No. 5,160,768 (Antoon), U.S. Pat. No. 5,254,354 (Stewart), U.S. Pat. No. 5,333,394 (Herdeman), U.S. Pat. No. 5,433,335 (Raudalus et al.), U.S. Pat. No. 5,460,841 (Herdeman), U.S. Pat. No. 5,556,658 (Raudalus et al.), U.S. Pat. No. 5,658,607 (Herdeman), U.S. Pat. No. 5,807,630 (Christie et al.), U.S. Pat. No. 6,013,293 (De Moor), U.S. Pat. No. 6,376,032 (Clarke et al.), U.S. Pat. No. 6,548,132 (Clarke et al.), and U.S. Pat. No. 6,579,607 (Gozukara et al.), copending commonly assigned U.S. patent application Ser. No. 09/858,190 (Publication Number US2002/0090425) and Ser. No. 09/989,682 (Publication Number US2002/0127305), Publication Number US2003/0099832, published 29 May, 2003, International Publication Nos. WO 94/12040 (Fresh Western), WO 96/38495 (Landec), WO 99/33658 (Gozukara et al.), WO 00/04787 (Landec) and WO 01/92118 (Landec), and European Patent Applications Nos. 0,351,115 and 0,351,116 (Courtaulds). The disclosure of each of those patents, applications and publications is incorporated herein by reference for all purposes.
The preferred packaging atmosphere for a respiring material often depends on the material and the changes (if any) in the material which are desired. In some cases, it is desirable for the packaging atmosphere to have a relatively high CO2 content and a relatively low O2 content. In order to obtain such a packaging atmosphere in a modified atmosphere package, it is desirable to make use of an ACM which has a relatively low COTR/OTR ratio (often referred to herein as the R ratio).
U.S. Pat. No. 5,807,630 (Christie et al.), U.S. Pat. No. 6,579,607 (Gozukara et al.) and Publication Number US 2003/0099832 (Borchardt), published May 29, 2003, disclose self-supporting films of controlled permeability which comprise a film-forming polymer and a porous filler. The filler has a particle size greater than the intrinsic film thickness of the film-forming polymer, and is present in amount sufficient to reduce the R ratio of the film.